Manufacturing method of compressed strip-shaped electrode plate

ABSTRACT

This manufacturing method is a method of manufacturing a compressed strip-shaped electrode plate. The method includes: a preliminary compression step of forming a pre-compressed strip-shaped electrode plate by roll-pressing an uncompressed strip-shaped electrode plate in which an uncompressed active material layer that is not yet compressed is formed on a current collector foil; an attraction and removal step of attracting and removing fine particles of active material particles from near a surface of a pre-compressed active material layer by an attracting magnet that is disposed so as to be separated from the pre-compressed active material layer in a thickness direction; and a main compression step of obtaining the compressed strip-shaped electrode plate by roll-pressing a particle-removed strip-shaped electrode plate from which the fine particles have been removed.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to Japanese Patent Application No.2020-077409 filed on Apr. 24, 2020, incorporated herein by reference inits entirety.

BACKGROUND 1. Technical Field

The present disclosure relates to a manufacturing method of a compressedstrip-shaped electrode plate and a manufacturing system of a compressedstrip-shaped electrode plate.

2. Description of Related Art

In manufacturing of a strip-shaped electrode plate including astrip-shaped current collector foil and a strip-shaped active materiallayer that contains active material particles and a binding agent andextends in a longitudinal direction, it is a conventionally knownpractice to increase the density of the active material layer byroll-pressing, and thereby compressing in a thickness direction, astrip-shaped (uncompressed) electrode plate that is formed by, forexample, applying and then drying an active material paste (e.g., seeJapanese Unexamined Patent Application Publication No. 2013-73690 andJapanese Unexamined Patent Application Publication No. 2015-90805).

SUMMARY

When the active material layer of a long strip-shaped electrode plate iscompressed in the thickness direction by roll-pressing, sometimes fineparticles of the active material particles stick little by little to apart of a surface of the press roll that presses the active materiallayer, and the thickness and area of sticking increase gradually overtime. If fine particles of the active material particles thus stick tothe press roll, the active material layer cannot be appropriatelydensified due to, for example, a dent formed in the roll-pressed activematerial layer at a position corresponding to the position of sticking.Thus, it is difficult to manufacture a compressed strip-shaped electrodeplate having an evenly densified compressed active material layer.

It has been learned that fine particles of active material particlessticking to the surface of a press roll include broken-off fineparticles that are fragments of active material particles having brokenoff from the active material particles, and small-diameter fineparticles that are those active material particles that have extremelysmall particle diameters, and that these fine particles adhere to thesurface of the press roll through the binding agent. When an activematerial layer is compressed by a press roll, the active material layeris subjected to not only a compressive force but also a shearing forcefrom the press roll. As active material particles present near thesurface of the active material layer are subjected to the compressiveforce or the shearing force, fragments of the active material particlesmay break off and turn into broken-off fine particles. Meanwhile, activematerial particles used for an active material layer range in particlediameter from small to large, and include also active material particlesthat have extremely small particle diameters of 2 μm or less(small-diameter fine particles). When the surface of the press rollcomes into pressure-contact with the surface of the active materiallayer, some of the broken-off fine particles and the small-diameter fineparticles present near the surface of the active material layer adhereto the surface of the press roll through the binding agent that adheresto these particles. Sticking of fine particles of active materialparticles to the surface of the press roll as described above seems tobe caused by such broken-off fine particles and small-diameter fineparticles repeatedly adhering to the surface of the press roll duringthe process of densification of a strip-shaped electrode plate using thepress roll.

The present disclosure has been made in view of such a problem andprovides a manufacturing method of a compressed strip-shaped electrodeplate and a manufacturing system of a compressed strip-shaped electrodeplate in which fine particles of active material particles are lesslikely to stick to the surfaces of press rolls when a strip-shapedelectrode plate is compressed by roll-pressing, and by which acompressed strip-shaped electrode plate having an evenly densifiedcompressed active material layer can be manufactured.

A first aspect of the present disclosure to solve the above problem is amanufacturing method of a compressed strip-shaped electrode plateincluding: a strip-shaped current collector foil; and a compressedactive material layer that contains active material particles that areattracted to a magnet, and a binding agent, and is formed on the currentcollector foil and compressed in a thickness direction of the currentcollector foil. This manufacturing method includes: a preliminarycompression step of forming a pre-compressed strip-shaped electrodeplate by roll-pressing, using first press rolls, an uncompressedstrip-shaped electrode plate in which an uncompressed active materiallayer that is not yet compressed is formed on the current collectorfoil; an attraction and removal step of attracting and removing fineparticles of the active material particles from near a surface of apre-compressed active material layer of the pre-compressed strip-shapedelectrode plate by an attracting magnet that is disposed so as to beseparated from the pre-compressed active material layer in the thicknessdirection; and a main compression step of obtaining the compressedstrip-shaped electrode plate by roll-pressing, using second press rolls,a particle-removed strip-shaped electrode plate from which the fineparticles have been removed in the attraction and removal step.

This manufacturing method includes, before the main compression step,the preliminary compression step of forming the pre-compressed activematerial layer by roll-pressing the uncompressed active material layerusing the first press rolls, and the attraction and removal step.Generally, near a surface of the uncompressed active material layer,active material particles are present from which, if the maincompression step is directly performed, fragments easily break off andturn into broken-off fine particles under a compressive force or ashearing force exerted by the second press rolls. In the technique ofthe present disclosure, preliminary compression using the first pressrolls is performed in the preliminary compression step to generatebroken-off fine particles from such active material particlesbeforehand. Then, in the attraction and removal step, the broken-offfine particles that have been generated beforehand in the preliminarycompression step and small-diameter fine particles that are those activematerial particles that have extremely small particle diameters areattracted and removed from near the surface of the pre-compressed activematerial layer by using the attracting magnet. As a result, thelikelihood that fine particles of active material particles may stick tothe second press rolls as in conventional methods can be reduced in themain compression step, so that a compressed strip-shaped electrode platehaving an evenly densified compressed active material layer can bemanufactured.

The term “compressed strip-shaped electrode plate” to be manufacturedcovers an electrode plate having a compressed active material layerprovided on one surface of the current collector foil, as well as anelectrode plate having a compressed active material layer provided oneach surface of the current collector foil. The same applies to theterms “uncompressed strip-shaped electrode plate,” “pre-compressedstrip-shaped electrode plate,” and “particle-removed strip-shapedelectrode plate.” The term “compressed active material layer” formed onthe current collector foil covers not only a strip-shaped compressedactive material layer that extends in the longitudinal direction of thecurrent collector foil but also, for example, a rectangular compressedactive material layer that is intermittently formed in the longitudinaldirection. The same applies to the terms “uncompressed active materiallayer,” “pre-compressed active material layer,” and “particle-removedactive material layer.”

The active material particles contained in the active material layer areactive material particles that are attracted to a magnet. Examples ofthe active material particles include positive-electrode active materialparticles that are attracted to a magnet because they are made of metaloxides including ferromagnetic Ni, Co, or Fe ions, such as LiCoO₂, Li(Ni_(1/3)Co_(1/3)Mn_(1/3))O₂, or LiFePO₄. The term “fine particles” ofactive material particles covers “broken-off fine particles” withparticle diameters of 2 μm or less that are fragments of active materialparticles having broken off under a compressive force or a shearingforce, and “small-diameter fine particles” that are those of activematerial particles that have particle sizes of 2 μm or less.

As the form of the “attracting magnet,” a round rod shape, a rectangularplate shape, etc. can be used. Specific examples of the “attractingmagnet” include a cylindrical magnet in which fan-shaped magnets eachhaving an N-pole and an S-pole formed respectively in one end surfaceand the other end surface in a circumferential direction are forcedlydisposed in a circle and fixed to one another, with the N-poles buttedtogether and the S-poles butted together, such that the magnetic polesof the N-pole and the S-pole appear alternately in a circumferentialdirection in an outer circumferential surface. Further, as the“attracting magnet,” a columnar, cylindrical, or prism-shaped(rectangular plate-shaped) magnet can also be used in which disc-shaped,ring-shaped, or rectangular plate-shaped magnets each having an N-poleand an S-pole formed respectively in one surface and the other surfacein a thickness direction are forcibly stacked and fixed to one anotherin the thickness direction, with the N-poles butted together and theS-poles butted together, such that the magnetic poles of the N-pole andthe S-pole appear alternately in a stacking direction (the thicknessdirection; an axial direction) in an outer side surface. In addition, asthe “attracting magnet,” a magnet that is obtained by covering a surfaceof the aforementioned magnets on the side of a pre-compressedstrip-shaped electrode plate with a member made of paramagnetic metal,plastic, or the like can also be used; for example, a magnet obtained byhousing the aforementioned cylindrical, columnar, or prism-shaped magnetin a tube, such as a cylinder or a rectangular cylinder, made ofparamagnetic metal (paramagnetic stainless steel (e.g., SUS304), copper,or the like that is not attracted to a magnet), plastic, such as PET oracryl, ceramic, such as alumina, or the like, and a magnet obtained byhousing the aforementioned magnets in a tube, such as a cylinder with abottom or a rectangular cylinder, made of paramagnetic metal, plastic,or the like.

The separation distance between the attracting magnet and thepre-compressed active material layer of the pre-compressed strip-shapedelectrode plate is set to such a distance that the attracting magnet canappropriately attract fine particles of the active material particlesfrom the surface of the pre-compressed active material layer. Theseparation distance can be adjusted as necessary according to thestrength of the magnetic force of the attracting magnet (specifically,the degree of a magnetic flux density in a surface of the attractingmagnet). The separation distance can be adjusted to be longer when thestrength of the magnetic force of the attracting magnet is higher and tobe shorter when the strength of the magnetic force is lower.

The preliminary compression step, the attraction and removal step, andthe main compression step can be performed separately in terms of timeor process by, for example, including, between steps, a reeling step ofreeling up a strip-shaped electrode plate in each stage onto a roll.However, it is also possible to manufacture a compressed strip-shapedelectrode plate by performing the preliminary compression step, theattraction and removal step, and the main compression step in this orderas a series of steps on an uncompressed strip-shaped electrode platethat is being transferred in the longitudinal direction.

Further, in the manufacturing method of a compressed strip-shapedelectrode plate, the preliminary compression step may use, as the firstpress rolls, magnet rolls with magnetic fields generated in surfaces ofthe magnet rolls.

In this manufacturing method, the preliminary compression step isperformed by using magnet rolls as the first press rolls. Thus, inpreliminary compression of the uncompressed active material layers inthe preliminary compression step, broken-off fine particles generated onthe surfaces of the pre-compressed active material layers andsmall-diameter fine particles present near the surfaces can bemagnetized by the magnetic fields, which helps attract and remove thesefine particles by the attracting magnet in the attraction and removalstep.

Examples of the magnet rolls used as the first press rolls includemagnet rolls obtained by integrating a cylindrical or columnar magnetwith magnetic poles formed in an outer surface into an outer cylinderthat is made of paramagnetic metal, such as stainless steel (e.g.,SUS304).

Further, in one of the above-described manufacturing methods of acompressed strip-shaped electrode plate, the preliminary compressionstep may use the first press rolls that have a smaller diameter than thesecond press rolls.

In roll-pressing, a larger shearing stress is applied to an object beingrolled when the press rolls have a smaller diameter D. In thismanufacturing method, the first press rolls have a smaller diameter thanthe second press rolls. In the preliminary compression step, a largershearing force can be applied to the uncompressed active material layerby using the first press rolls that have a smaller diameter than thesecond press rolls than by using the first press rolls that have thesame diameter as the second press rolls or a larger diameter than thesecond press rolls. Thus, active material particles which are presentnear the surface of the uncompressed active material layer and fromwhich fragments may break off when a compressive force or a shearingforce is applied can be subjected to a large shearing force in thepreliminary compression step to thereby cause fragments of the activematerial particles to break off and turn into broken-off fine particlesbeforehand, so as to be removed in the attraction and removal step. Thiscan further reduce the likelihood that broken-off fine particles may begenerated from active material particles and stick to the second pressrolls in the main compression step.

Further, in one of the above-described manufacturing methods of acompressed strip-shaped electrode plate, a preliminary load that isapplied to the uncompressed active material layer using the first pressrolls in the preliminary compression step may be set to be smaller thana main load that is applied to the particle-removed active materiallayer using the second press rolls in the main compression step.

In this manufacturing method, the preliminary load is set to be smallerthan the main load, which can reduce the likelihood that broken-off fineparticles generated in the preliminary compression step andsmall-diameter fine particles contained in the uncompressed activematerial layers near the surfaces thereof may stick to the first pressrolls by coming into strong pressure-contact with the first press rollsthrough the binding agents.

Further, in one of the above-described manufacturing methods of acompressed strip-shaped electrode plate, the preliminary compressionstep, the attraction and removal step, and the main compression step maybe performed in this order on the uncompressed strip-shaped electrodeplate that is being transferred in a longitudinal direction of thecurrent collector foil.

In this manufacturing method, the steps are sequentially performed as aseries of steps on the uncompressed strip-shaped electrode plate, sothat the compressed strip-shaped electrode plate can be easily obtained.

Another aspect of the present disclosure to solve the above problem is amanufacturing system of a compressed strip-shaped electrode plateincluding: a strip-shaped current collector foil; and a compressedactive material layer that contains active material particles that areattracted to a magnet, and a binding agent, and is formed on the currentcollector foil and compressed in a thickness direction of the currentcollector foil. This manufacturing system includes: a preliminarycompression unit that has a first roll press machine using first pressrolls and, by the first roll press machine, compresses, in the thicknessdirection, an uncompressed strip-shaped electrode plate in which anuncompressed active material layer that is not yet compressed is formedon the current collector foil; an attraction and removal unit that hasan attracting magnet disposed so as to be separated in the thicknessdirection from a pre-compressed active material layer of apre-compressed strip-shaped electrode plate formed in the preliminarycompression unit, and that attracts and removes fine particles of theactive material particles from near a surface of the pre-compressedactive material layer; and a main compression unit that has a secondroll press machine using second press rolls and, by the second rollpress machine, compresses, in the thickness direction, aparticle-removed strip-shaped electrode plate from which the fineparticles have been removed by the attraction and removal unit.

This manufacturing system includes, other than the main compressionunit, the preliminary compression unit and the attraction and removalunit. Before compression by the second roll press machine in the maincompression unit, broken-off fine particles are generated by preliminarycompression in the preliminary compression unit and the broken-off fineparticles and small-diameter fine particles are attracted and removed inthe attraction and removal unit. As a result, fine particles of theactive material particles are less likely to stick to the second pressrolls used in the second roll press machine of the main compressionunit, so that a compressed strip-shaped electrode plate having an evenlydensified compressed active material layer can be manufactured.

In the manufacturing system of a compressed strip-shaped electrodeplate, the preliminary compression unit may use, as the first pressrolls, magnet rolls with magnetic fields generated in surfaces of themagnet rolls.

In this manufacturing system, magnet rolls are used as the first pressrolls. Thus, in preliminary compression of the uncompressed activematerial layer in the preliminary compression unit, broken-off fineparticles generated on the surface of the pre-compressed active materiallayer and small-diameter fine particles present near the surface can bemagnetized by the magnetic fields, which further helps attract andremove these fine particles by the attracting magnet in the attractionand removal unit.

Further, in one of the above-described manufacturing systems of acompressed strip-shaped electrode plate, the preliminary compressionunit may use the first press rolls that have a smaller diameter than thesecond press rolls.

In this manufacturing system, the first press rolls (magnet rolls) havea smaller diameter than the second press rolls. In the preliminarycompression unit, a larger shearing force can be applied to theuncompressed active material layers by using the first press rolls thathave a smaller diameter than the second press rolls than by using thefirst press rolls that have the same diameter as the second press rollsor a larger diameter than the second press rolls. Thus, active materialparticles which are present near the surfaces of the uncompressed activematerial layers and from which fragments may break off when acompressive force or a shearing force is applied can be subjected to alarge shearing force in the preliminary compression unit to therebycause fragments of the active material particles to break off and turninto broken-off fine particles beforehand, so as to be removed in theattraction and removal unit. This can further reduce the likelihood thatbroken-off fine particles that are fragments having broken off fromactive material particles may stick to the second press rolls in themain compression unit.

Further, one of the above-described manufacturing systems of acompressed strip-shaped electrode plate may further include a transferunit that transfers the uncompressed strip-shaped electrode plate in thelongitudinal direction, and the preliminary compression unit, theattraction and removal unit, and the main compression unit may bedisposed so as to perform processes in this order on the uncompressedstrip-shaped electrode plate that is being transferred by the transferunit.

In this manufacturing system, processes in the respective units aresequentially performed as a series of processes on the uncompressedstrip-shaped electrode plate, so that a compressed strip-shapedelectrode plate can be easily obtained.

BRIEF DESCRIPTION OF THE DRAWINGS

Features, advantages, and technical and industrial significance ofexemplary embodiments of the disclosure will be described below withreference to the accompanying drawings, in which like signs denote likeelements, and wherein:

FIG. 1 is a view illustrating a manufacturing system of a compressedstrip-shaped positive electrode plate according to an embodiment;

FIG. 2 is a view according to the embodiment, illustrating how anuncompressed strip-shaped electrode plate is roll-pressed by first pressrolls to form a pre-compressed positive electrode plate in a preliminarycompression unit;

FIG. 3 is a view according to the embodiment, illustrating how fineparticles of active material particles are attracted and removed from asurface of a pre-compressed active material layer by attracting magnetsin an attraction and removal unit;

FIG. 4 is a view according to the embodiment, illustrating how aparticle-removed positive electrode plate is roll-pressed by secondpress rolls to form a compressed strip-shaped electrode plate in a maincompression unit; and

FIG. 5 is a flowchart of steps according to the embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

An embodiment of the present disclosure will be described below withreference to FIG. 1 to FIG. 5. A manufacturing system 1 (see FIG. 1)according to this embodiment is a manufacturing system that manufacturesa compressed positive electrode plate PPE by compressing an uncompressedpositive electrode plate UPE in a thickness direction TD of a currentcollector foil CF.

The uncompressed positive electrode plate UPE (see also FIG. 2) has thecurrent collector foil CF that is made of aluminum and has a stripshape, and uncompressed active material layers UAM that are formedrespectively on both surfaces of the current collector foil CF, at acentral part in a width direction (a direction orthogonal to the sheetplanes of FIG. 1 and FIG. 2), except for both end portions in the widthdirection, in a strip shape extending in a longitudinal direction LD ofthe current collector foil CF. The uncompressed active material layersUAM contain active material particles AM that are attracted to a magnet,and a binding agent BD. Specifically, the uncompressed active materiallayers UAM contain positive-electrode active material particles made ofLi (Ni_(1/3)Co_(1/3)Mn_(1/3))O₂ as the active material particles AM, andalso PVDF as the binding agent BD and acetylene black as a conductionpromoting agent. (So do a pre-compressed active material layer YAM, aparticle-removed active material layer RAM, and a compressed activematerial layer PAM, all to be described later.) The active materialparticles AM made of Li (Ni_(1/3)Co_(1/3)Mn_(1/3))O₂ are a metal oxidecontaining ferromagnetic Ni, Co, and Fe ions and has the property ofbeing attracted to a magnet. The active material particles AM used forthe uncompressed active material layer UAM etc. range in particlediameter from a small particle diameter to a large one, with a peakroughly at an average particle diameter. (The active material particlesAM are represented by while circles with various diameters in FIG. 2 toFIG. 4). For example, the active material particles AM used in thisembodiment have an average particle diameter of 10 μm and include activematerial particles AM roughly within a range of particle diameters of 1μm to 15 μm. The active material particles AM include about 3 wt % offine particles having particle diameters of 2 μm or less. (Hereinafter,such fine particles will be referred to as small-diameter fine particlesAMD.)

The uncompressed positive electrode plate UPE is formed by, for example,applying an active material paste (not shown) containing a solvent, theactive material particles AM, the binding agent BD, etc. to the centralpart of the current collector foil CF in the width direction and dryingthis active material paste. It is also possible to form the uncompressedpositive electrode plate UPE by creating a mass of wet granularmaterials including a solvent, the active material particles AM, thebinding agent BD, etc., forming an active material paste layer bytransferring the mass onto a transfer roll while compressing the mass,further transferring the active material paste layer onto the currentcollector foil CF, and then drying the active material paste layer.

In this embodiment, an example is shown in which an uncompressedpositive electrode plate that has the uncompressed active material layerUAM on each surface of the current collector foil CF is used as theuncompressed positive electrode plate UPE. However, an uncompressedpositive electrode plate that has the uncompressed active material layerUAM on only one surface of the current collector foil CF, or anuncompressed positive electrode plate that has the compressed activematerial layer PAM that has been already compressed on one surface ofthe current collector foil CF and has the uncompressed active materiallayer UAM on only the other surface can also be used as the uncompressedpositive electrode plate UPE.

The manufacturing system 1 of this embodiment is composed of apreliminary compression unit 10, an attraction and removal unit 20, amain compression unit 30, a transfer unit 40, and a reeling unit 50 (seealso FIG. 2 to FIG. 4). Of these components, the transfer unit 40 hastransfer rollers 41, 42, 43 and, as shown in FIG. 1, delivers anelectrode plate in each stage, such as the uncompressed positiveelectrode plate UPE, to the reeling unit 50 by transferring theelectrode plate in a longitudinal direction LD (transfer direction CD)using the transfer rollers 41, 42, 43. The manufacturing system 1 canimplement a manufacturing method of the compressed positive electrodeplate PPE in which a preliminary compression step S1, an attraction andremoval step S2, a main compression step S3, and a reeling step S4 areperformed in this order (see FIG. 5).

The preliminary compression unit 10 (see also FIG. 2) of themanufacturing system 1 forms a pre-compressed positive electrode plateYPE by compressing the strip-shaped uncompressed positive electrodeplate UPE in the thickness direction TD while transferring thestrip-shaped uncompressed positive electrode plate UPE using a transferroller 2 etc. in the transfer direction CD that coincides with thelongitudinal direction LD of the current collector foil CF.Specifically, the preliminary compression unit 10 has a first roll pressmachine 11 that uses a pair of first press rolls 12, 13 and, by thefirst roll press machine 11, compresses, in the thickness direction TD,the uncompressed positive electrode plate UPE which has a strip shapeextending in the longitudinal direction LD and in which the uncompressedactive material layers UAM that are not yet compressed in the thicknessdirection TD are formed. Thus, the preliminary compression step S1 offorming the pre-compressed positive electrode plate YPE by roll-pressingthe uncompressed positive electrode plate UPE using the first pressrolls 12, 13 is performed in the preliminary compression unit 10.

As a result of this preliminary compression, the uncompressed positiveelectrode plate UPE having a thickness T1 turns into the pre-compressedpositive electrode plate YPE having a thickness T2 smaller than thethickness T1 (T2<T1), and the uncompressed active material layer UAMhaving a thickness TA1 turns into the pre-compressed active materiallayer YAM having a thickness TA2 smaller than the thickness TA1(TA2<TA1).

When the uncompressed positive electrode plate UPE is roll-pressed bythe pair of first press rolls 12, 13 in the preliminary compression stepS1 that is performed using the preliminary compression unit 10, acompressive force and a shearing force are applied to the uncompressedactive material layers UAM of the uncompressed positive electrode plateUPE. In particular, a large shearing force tends to be applied from thefirst press rolls 12, 13 to those of the active material particles AMcontained in each uncompressed active material layer UAM (represented bywhite circles in FIG. 2 to FIG. 4) that are located near a surface UAMSof the uncompressed active material layer UAM. Then, fragments break offfrom the active material particles AM and thus broken-off fine particlesAMM (represented by small black circles in FIG. 2 and FIG. 3) that havesmall sizes (particle diameters of 2 μm or less) are generated. Sincethe broken-off fine particles AMM are also bonded to other activematerial particles AM etc. in the pre-compressed active material layersYAM through the binding agents BD, the broken-off fine particles AMMremain on surfaces YAMS of the pre-compressed active material layers YAMwithout moving to outer circumferential surfaces 12S, 13S of the firstpress rolls 12, 13.

Further, in this embodiment, as shown in FIG. 2, magnet rolls withmagnetic fields generated in the outer circumferential surfaces 12S, 13Sare used as the pair of first press rolls 12, 13 used in the first rollpress machine 11. Specifically, the first press rolls 12, 13 are formedby inserting and fixing, and thereby integrating, a magnet core 15inside a cylindrical outer cylinder 14 made of paramagnetic stainlesssteel (SUS304). The magnet core 15 is composed of an even number offan-shaped magnets 15M that have a fan-shaped cross-section and areelongated in an axial direction of the first press rolls 12, 13 (thewidth direction of the current collector foil CF; a directionperpendicular to the sheet plane of FIG. 2) and that are magnetized suchthat each magnet 15M has an N-pole and an S-pole formed respectively inend surfaces 15MT in a circumferential direction. These magnets 15M arecombined into a cylindrical shape and fixed to one another, with theN-poles butted together and the S-poles butted together, so as to form apattern in which the magnetic poles of the N-pole and the S-pole appearalternately in a circumferential direction in an outer circumferentialsurface 15S of the magnet core 15. Thus, the magnetic poles of theN-pole and the S-pole also appear alternately in a circumferentialdirection in an outer circumferential surface 14S of the outer cylinder14, i.e., the outer circumferential surfaces 12S, 13S of the first pressrolls 12, 13.

A magnetic flux density B10 at the magnetic poles formed in the outercircumferential surfaces 12S, 13S of the first press rolls 12, 13 is setto be, for example, lower than 0.1 T (=1000 G), specifically, 0.08 T,which is not higher than a tenth of a magnetic flux density in outercircumferential surfaces 21S, 22S of magnet bars 21, 22 used in theattraction and removal unit 20 to be described next.

Thus, in the preliminary compression unit 10 and the preliminarycompression step S1 using the preliminary compression unit 10 of thisembodiment, the first press rolls 12, 13 (magnet rolls) having theintegrated magnet core (magnet) 15 are used. This makes it possible toform the pre-compressed positive electrode plate YPE that ispreliminarily compressed and, at the same time, to magnetize thebroken-off fine particles AMM generated on the surface YAMS of thepre-compressed active material layer YAM and the small-diameter fineparticles AMD present near the surface YAMS by the magnetic fieldsgenerated in the first press rolls 12, 13, which helps attract andremove these fine particles by the magnet bars 21, 22 in the attractionand removal step S2 to be described next.

To prevent wear of the outer cylinder 14, a hard plating layer 14Mformed by a hard chrome plating is formed on the outer circumferentialsurface 14S of the outer cylinder 14. Instead of thus providing the hardplating layer 14M on the outer circumferential surface 14S of the outercylinder 14, a surface treatment for hardening the surface of the outercylinder 14 according to the material may also be performed.

As can be easily understood from FIG. 1, FIG. 2, and FIG. 4, in themanufacturing system 1 of this embodiment, a diameter D1 of the pair offirst press rolls 12, 13 used in the preliminary compression unit 10 isset to be smaller than a diameter D2 of a pair of second press rolls 32,33 used in the main compression unit 30 to be described later (D1<D2).Specifically, the diameter D1 is set to be about 1/2.5 of the diameterD2 (D1=D2/2.5).

Generally, in roll-pressing, a larger shearing stress is applied to anobject being rolled when the press rolls have a smaller diameter D. Inthe manufacturing system 1, the diameter D1 of the first press rolls 12,13 is set to be smaller than the diameter D2 of the second press rolls32, 33 (D1<D2). In the preliminary compression step S1 using thepreliminary compression unit 10, a larger shearing force can be appliedto the uncompressed active material layers UAM by using the first pressrolls 12, 13 that have a smaller diameter than the second press rolls(D1<D2) as in this embodiment than by using the first press rolls thathave the same diameter as the second press rolls (D1=D2) or a largerdiameter than the second press rolls (D1>D2).

Thus, the active material particles AM which are present near thesurfaces UAMS of the uncompressed active material layers UAM and fromwhich fragments may break off can be subjected to a large shearing forcein the preliminary compression unit 10 to thereby cause fragments tobreak off and turn into the broken-off fine particles AMM beforehand, soas to be removed by the magnet bars 21, 22 of the attraction and removalunit 20. This can further reduce the likelihood that the broken-off fineparticles AMM may be generated from the active material particles AM andstick to the second press rolls 32, 33 in the main compression unit 30.

The diameter D1 is preferably within a range of ¼ to ¾ of the diameterD2. When the diameter D1 is smaller than ¼ of the diameter D2, thediameter D1 of the first press rolls 12, 13 is relatively so small thata large shearing force is applied to the uncompressed active materiallayers UAM and the active material particles break easily, which mayresult in excessive generation of broken-off fine particles AMM. On theother hand, when the diameter D1 is larger than ¾ of the diameter D2,the diameter D1 of the first press rolls 12, 13 is relatively large, sothat a small shearing force is applied to the uncompressed activematerial layers UAM, which makes it difficult to appropriately generatethe broken-off fine particles AMM and may result in an increased amountof fine particles AMS sticking to the second press rolls 32, 33 in themain compression step S3.

In the preliminary compression step S1 of this embodiment, a preliminaryload F1 that is applied to compress the uncompressed active materiallayers UAM using the first press rolls 12, 13 in the preliminarycompression step S1 is set to be smaller than a main load F2 that isapplied to the particle-removed active material layers RAM using thesecond press rolls 32, 33 in the main compression step S3 to bedescribed later (F1<F2). Specifically, in this embodiment, thepreliminary load F1 is set to 2.3×10⁵ N/m, which is smaller than themain load F2 (F2=4.6×10⁵ N/m).

A possible explanation for why the fine particles AMS, such as thebroken-off fine particles AMM and the small-diameter fine particles AMD,move from the active material layers and stick to the press rolls isthat, as the fine particles AMS come into strong pressure-contact withthe press rolls through the binding agents BD, the strength with whichthe fine particles AMS adhere to the press rolls becomes larger than thestrength with which the fine particles AMS adhere to other activematerial particles AM inside the active material layers. Based on this,the preliminary load F1 is set to be smaller than the main load F2(F1<F2) in the manufacturing method of this embodiment. Thus, the fineparticles AMS, such as the broken-off fine particles AMM generated inthe preliminary compression step S1 and the small-diameter fineparticles AMD contained in the uncompressed active material layers UAMnear the surfaces UAMS, are less likely to come into strongpressure-contact with the first press rolls 12, 13 through the bindingagents BD. As a result, the likelihood that the fine particles AMS maymove from the uncompressed active material layers UAM to the first pressrolls 12, 13 and stick to the first press rolls 12, 13 can be reduced.

The preliminary load F1 is preferably within a range of ¼ to ⅔ of themain load F2. When the load F1 is smaller than ¼ of the load F2, theload F1 applied to the first press rolls 12, 13 is so small that notonly is a small amount of broken-off fine particles AMM generated in thepreliminary compression step S1 but also it is unavoidable to increasethe load F2 applied in the main compression step S3 to obtain thecompressed positive electrode plate PPE having a desired thickness T3.Then, even when the fine particles AMS are removed in the attraction andremoval step S2, the broken-off fine particles AMM are generated in themain compression step S3. Therefore, although sticking of fine particlesto the press rolls is mitigated compared with that in conventionalmethods, the broken-off fine particles AMM are more likely to stick tothe second press rolls 32, 33. On the other hand, when the load F1 issmaller than ⅔ of the load F2, the load F1 applied to the first pressrolls 12, 13 is so large that, in the preliminary compression step S1,many active material particles AM break and an excessively large amountof broken-off fine particles AMM is generated, which makes the troubleof the broken-off fine particles AMM sticking to the first press rolls12, 13 more likely.

Next, the attraction and removal unit 20 (see FIG. 1 and FIG. 3) of themanufacturing system 1 performs the attraction and removal step S2 offorming a particle-removed positive electrode plate RPE by attractingand removing the fine particles AMS of the active material particles AMfrom near the surfaces YAMS of the pre-compressed active material layersYAM of the strip-shaped pre-compressed positive electrode plate YPE,formed in the preliminary compression unit 10 (preliminary compressionstep S1), by the round-rod-shaped magnet bars 21, 22 while transferringthe pre-compressed positive electrode plate YPE in the longitudinaldirection LD (transfer direction CD).

The magnet bars 21, 22 used in the attraction and removal unit 20 have amagnetic force that is stronger than the magnetic force generated in thefirst press rolls 12, 13 that are magnet rolls, and are disposed so asto be separated from the pre-compressed active material layers YAM byseparation distances LL1, LL2, respectively. In this embodiment, thestrength of the magnetic force of the magnet bars 21, 22 (a magneticflux density B20 in the outer circumferential surfaces 21S, 22S of themagnet bars 21, 22) and the separation distances LL1, LL2 are selectedwithin such ranges that the broken-off fine particles AMM on thesurfaces YAMS of the pre-compressed active material layers YAM can beattracted and that the small-diameter fine particles AMD among theactive material particles AM present near the surfaces YAMS of thepre-compressed active material layers YAM can be attracted. (In thisembodiment, LL1=LL2). Specifically, in this embodiment, the magnet bars21, 22 having a magnetic flux density B20 of, for example, 1 T to 1.8 T(10000 G to 18000 G) are used, and the separation distances LL1, LL2 areselected within a range of about 2 mm to 8 mm.

Thus, in the attraction and removal unit 20, when the pre-compressedpositive electrode plate YPE is transferred in the longitudinaldirection LD, the broken-off fine particles AMM (having the property ofbeing attracted to a magnet) that are formed in the preliminarycompression unit 10 and present on the surfaces YAMS of thepre-compressed active material layers YAM are attracted by the magneticforces of the magnet bars 21, 22 and move to the magnet bars 21, 22 byflying across the space. As a result, the broken-off fine particles AMMare removed from the surfaces YAMS of the pre-compressed active materiallayers YAM.

In addition, some of the small-diameter fine particles AMD of the activematerial particles AM (having the property of being attracted to amagnet) that are present near the surfaces YAMS of the pre-compressedactive material layers YAM are also attracted by the magnetic forces ofthe magnet bars 21, 22 and move to the magnet bars 21, 22 by flyingacross the space. As a result, some of the small-diameter fine particlesAMD are also removed from near the surfaces YAMS of the pre-compressedactive material layers YAM. Among the active material particles AM, thesmall-diameter fine particles AMD having small particle diameters havealso small surface areas, and some of the small-diameter fine particlesAMD are bonded to other active material particles AM in thepre-compressed active material layers YAM through the binding agents BDwith a small force. Therefore, when attracted by the strong magneticforces of the magnet bars 21, 22, some of the small-diameter fineparticles AMD move from near the surfaces YAMS of the pre-compressedactive material layers YAM to the magnet bars 21, 22 by flying acrossthe space. In this way, the fine particles AMS of the active materialparticles AM are attracted and removed from near the surfaces YAMS ofthe pre-compressed active material layers YAM to form theparticle-removed positive-electrode plate having the particle-removedactive material layers RAM. As shown in FIG. 3 and FIG. 4, inside eachparticle-removed active material layer RAM on an inner side from thevicinity of the surface RAMS (on the side of the current collector foilCF), the small-diameter fine particles AMD remain without being removed.

As shown in FIG. 3, as the magnet bars 21, 22 of this embodiment,round-rod-shaped magnets (attracting magnets) with magnetic fieldsgenerated in the outer circumferential surfaces 21S, 22S are used, andthese magnets are used by being rotated in a forward direction indicatedby the arrow in FIG. 3. Specifically, the magnet bars 21, 22 of thisembodiment are formed by inserting a magnet core 24 into a cylindricalouter cylinder 23 that is made of paramagnetic stainless steel (SUS304).The magnet core 24 is composed of an even number of fan-shaped magnets24M that have a fan-shaped cross-section and are elongated in an axialdirection of the magnet bars 21, 22 (the width direction of the currentcollector foil CF; a direction perpendicular to the sheet plane of FIG.3) and that each have magnetic poles of an N-pole and an S-pole formedrespectively in end surfaces 24MT in a circumferential direction. Thesemagnets 24M are combined into a cylindrical shape and fixed to oneanother such that the N-poles are butted together and the S-poles arebutted together. Thus, the magnet core 24 is a magnet in which themagnetic poles of the N-pole and the S-pole appear alternately in acircumferential direction in an outer circumferential surface 24S.Therefore, the magnetic poles are formed also in an outercircumferential surface 23S of the outer cylinder 23, i.e., the outercircumferential surfaces 21S, 22S of the magnet bars 21, 22, in such apattern that the N-pole and the S-pole appear alternately in acircumferential direction. The magnetic flux density B20 at the magneticpoles formed in the outer circumferential surfaces 21S, 22S of themagnet bars 21, 22 is set to be, for example, 1 T to 1.8 T,specifically, 1 T, which is not lower than ten times the magnetic fluxdensity in the outer circumferential surfaces 12S, 13S of the firstpress rolls 12, 13 used in the preliminary compression unit 10.

Moreover, unlike the magnet cores 15 of the first press rolls 12, 13,the magnet cores 24 of the magnet bars 21, 22 can be inserted into andextracted from the outer cylinders 23. As described above, the fineparticles AMS of the active material particles AM composed of thebroken-off fine particles AMM and the small-diameter fine particles AMDare sucked up onto the outer circumferential surfaces 21S, 22S of themagnet bars 21, 22 by the magnetic force. As the fine particles AMS ofthe active material particles AM gradually build up on the outercircumferential surfaces 21S, 22S, it is necessary to remove the fineparticles AMS of the active material particles AM from the outercircumferential surfaces 21S, 22S at an appropriate timing, such asafter operation or during maintenance of the manufacturing system 1.While it is preferable that strong magnets be used as the magnet bars21, 22, using strong magnets makes it conversely difficult to remove thefine particles AMS of the active material particles AM that have beensucked up onto the outer circumferential surfaces 21S, 22S. However, inthe magnet bars 21, 22 of this embodiment, when the magnet cores 24 areextracted from the paramagnetic outer cylinders 23, the outer cylinders23 lose their magnetic properties, so that the fine particles AMS of theactive material particles AM can be easily removed from the outercircumferential surfaces 23S of the outer cylinders 23, i.e., from theouter circumferential surfaces 21S, 22S of the magnet bars 21, 22.

In the magnet bars 21, 22 of this embodiment, the outer cylinders 23made of paramagnetic SUS304 are used and the magnet cores 24 areintegrated inside the outer cylinders 23. Alternatively, the magnetcores 24 housed in cylinders made of other paramagnetic metal, such ascopper, plastic cylinders, or ceramic cylinders can also be used.

The main compression unit 30 (see FIG. 1 and FIG. 4) of themanufacturing system 1 forms the compressed positive electrode plate PPEby compressing, in the thickness direction TD, the strip-shapedparticle-removed positive electrode plate RPE that has already beenpreliminarily compressed, while transferring the particle-removedpositive electrode plate RPE in the longitudinal direction LD (transferdirection CD). Specifically, the main compression unit 30 has a secondroll press machine 31 that uses the pair of second press rolls 32, 33and, by the second roll press machine 31, compresses, in the thicknessdirection, the particle-removed positive electrode plate RPE in whichthe strip-shaped particle-removed active material layers RAM extendingin the longitudinal direction LD are formed on the current collectorfoil CF. Thus, the main compression step S3 of forming the compressedpositive electrode plate PPE by roll-pressing the particle-removedpositive electrode plate RPE using the second press rolls 32, 33 isperformed in the main compression unit 30.

As a result of main compression, the particle-removed positive electrodeplate RPE having the thickness T2 turns into the compressed positiveelectrode plate PPE having the thickness T3 smaller than the thicknessT2 (T3<T2). As a result of main compression, the particle-removed activematerial layers RAM having the thickness TA2 turn into the compressedactive material layers PAM having a thickness TA3 smaller than thethickness TA2 (TA3<TA2).

As in the preliminary compression step S1 in the preliminary compressionunit 10, when the particle-removed positive electrode plate RPE isroll-pressed by the pair of second press rolls 32, 33 in the maincompression step S3 in the main compression unit 30, a compressive forceand a shearing force are applied also to the particle-removed activematerial layers RAM. However, of the active material particles AM(represented by white circles in FIG. 4) contained in theparticle-removed active material layers RAM, those active materialparticles AM that are located near surfaces RAMS have already beensubjected to a large shearing force from the first press rolls 12, 13 inthe preliminary compression step S1. As a result, fragments of theactive material particles AM that have tended to break when a shearingforce or the like is applied have already broken off from the activematerial particles AM and turned into the broken-off fine particles AMMin the preliminary compression step S1, and thus these active materialparticles AM have become active material particles AM that do not easilybreak. Therefore, when a shearing force or the like is applied to theactive material particles AM located near the surfaces RAMS of theparticle-removed active material layers RAM in the main compression stepS3, fragments of these active material particles AM are less likely tobreak off and turn into the broken-off fine particles AMM. In addition,some of the small-diameter fine particles AMD have also been removedfrom near the surfaces RAMS of the particle-removed active materiallayers RAM.

Thus, in the main compression step S3 in the main compression unit 30,the fine particles AMS of the active material particles AM such as thebroken-off fine particles AMM and the small-diameter fine particles AMDare less likely to stick to the outer circumferential surfaces 32S, 33Sof the pair of second press rolls 32, 33 through the binding agents BD.As a result, the compressed positive electrode plate PPE having theevenly densified compressed active material layers PAM can bemanufactured.

The reeling unit 50 (see FIG. 1) of the manufacturing system 1 has areeling roll 51 onto which the strip-shaped compressed positiveelectrode plate PPE that has been formed in the main compression unit 30(main compression step S3) and transferred by the transfer rollers 42,43 in the longitudinal direction LD (transfer direction CD) is reeledup, and performs the reeling step S4 of reeling up the compressedpositive electrode plate PPE having been transferred via the transferrollers 42, 43 onto the reeling roll 51.

This completes the compressed positive electrode plate PPE that has beenreeled up onto the reeling roll 51 so as to be transportable.

In manufacturing of the compressed positive electrode plate PPE usingthe manufacturing system 1, the preliminary compression unit 10, theattraction and removal unit 20, and the main compression unit 30 aredisposed so as to perform the processes in this order on theuncompressed positive electrode plate UPE that is being transferred bythe transfer unit 40. Accordingly, the preliminary compression step S1,the attraction and removal step S2, and the main compression step S3 areperformed in this order on the uncompressed positive electrode plate UPEthat is being transferred in the longitudinal direction LD of thecurrent collector foil CF.

Thus, in the manufacturing system 1, the processes in the respectiveunits 10, 20, 30 are sequentially performed as a series of processes onthe uncompressed positive electrode plate UPE, so that the compressedpositive electrode plate PPE can be easily obtained. Moreover, sincesteps S1 to S3 are sequentially performed as a series of steps, thecompressed positive electrode plate PPE can be easily obtained.

While the present disclosure has been described above based on theembodiment, the embodiment and examples disclosed herein are in everyrespect merely illustrative and not restrictive. The technical scopedefined by the claims includes all changes that are equivalent inmeaning and scope to the claims.

For example, in the example shown in the embodiment, the compressedpositive electrode plate PPE (compressed strip-shaped electrode plate)is manufactured in which the strip-shaped compressed active materiallayer PAM extending in the longitudinal direction LD of the currentcollector foil CF is formed on each surface of the strip-shaped currentcollector foil CF (see FIG. 1). However, a compressed positive electrodeplate (compressed strip-shaped electrode plate) may be manufactured inwhich a compressed active material layer having, for example, arectangular shape, is intermittently formed in the longitudinaldirection LD on one surface or both surfaces of the strip-shaped currentcollector foil CF.

In the example shown in the embodiment, the cylindrical magnet cores 24formed by combining the fan-shaped magnets 24M and integrated inside thecylindrical outer cylinders 23 are used as the magnet bars 21, 22(attracting magnets). Instead of the magnet bars 21, 22, the cylindricalmagnet cores 24 can also be used as they are without using the outercylinders 23. Further, instead of the magnet bars 21, 22, prism-shaped(rectangular plate-shaped) magnets with magnetic poles formed on a sidefacing the pre-compressed positive electrode plate YPE may be used asattracting magnets as they are or by being inserted into rectangularcylindrical outer cylinders made of a paramagnetic material.

In the example shown in the embodiment, the pair of magnet bars 21, 22are disposed at opposite positions with the pre-compressed positiveelectrode plate YPE interposed therebetween as indicated by solid linesin FIG. 1. However, when the magnet bars 21, 22 are thus disposed, alarge attracting force or repulsing force acts between the magnet bars21, 22, which makes it necessary to provide a strong holding structure(not shown) for the magnet bars 21, 22. Therefore, the installationpositions of the magnet bar 21 and the magnet bar 22 may be moved awayfrom each other in the transfer direction CD so as to be separated fromeach other; for example, the magnet bar 22 may be disposed on adownstream side CDD in the transfer direction CD relatively to themagnet bar 21 as indicated by a dashed line in FIG. 1. Also in thiscase, as in the embodiment, the magnet bars 21, 22 are disposed at theseparation distance LL1, LL2, respectively, from the surfaces YAMS ofthe pre-compressed active material layers YAM at which the magnet bars21, 22 can appropriately attract and remove the fine particles AMS ofthe active material particles AM.

In the embodiment, the compressed positive electrode plate PPE in whichthe compressed active material layer PAM formed in a strip shape isformed on each surface of the strip-shaped current collector foil CF, ata central part in the width direction, except for both end portions inthe width direction is formed in the main compression unit 30 (maincompression step S3), and this compressed positive electrode plate PPEis directly reeled up onto the reeling roll 51. However, after thecompressed positive electrode plate PPE is formed in the maincompression unit 30, a slitting process of cutting the compressedpositive electrode plate PPE in half at the center in the widthdirection may be performed to form two strips of strip-shaped positiveelectrode plates, and these positive electrode plates may berespectively reeled up onto reeling rolls.

What is claimed is:
 1. A manufacturing method of a compressedstrip-shaped electrode plate including: a strip-shaped current collectorfoil; and a compressed active material layer that contains activematerial particles that are attracted to a magnet, and a binding agent,and is formed on the current collector foil and compressed in athickness direction of the current collector foil, the manufacturingmethod comprising: a drying step of drying an active material layer ontothe current collector foil before a preliminary compression step; thepreliminary compression step of forming a pre-compressed strip-shapedelectrode plate by roll-pressing, using first press rolls, anuncompressed strip-shaped electrode plate in which an uncompressedactive material layer that is not yet compressed is formed on thecurrent collector foil; an attraction and removal step of attracting andremoving fine particles of the active material particles from near asurface of a pre-compressed active material layer of the pre-compressedstrip-shaped electrode plate by an attracting magnet that is disposed soas to be separated from the pre-compressed active material layer in thethickness direction; and a main compression step of obtaining thecompressed strip-shaped electrode plate by roll-pressing, using secondpress rolls, a particle-removed strip-shaped electrode plate from whichthe fine particles have been removed in the attraction and removal step.2. The manufacturing method of a compressed strip-shaped electrode plateaccording to claim 1, wherein the preliminary compression step uses, asthe first press rolls, magnet rolls with magnetic fields generated insurfaces of the magnet rolls.
 3. The manufacturing method of acompressed strip-shaped electrode plate according to claim 1, whereinthe preliminary compression step uses the first press rolls that have asmaller diameter than the second press rolls.
 4. The manufacturingmethod of a compressed strip-shaped electrode plate according to claim1, wherein a preliminary load that is applied to the uncompressed activematerial layer using the first press rolls in the preliminarycompression step is set to be smaller than a main load that is appliedto the particle-removed active material layer using the second pressrolls in the main compression step.